This invention relates to cemented carbide materials for use in milling, turning and like cutting operations.
Usual cemented carbides for a cutting operation such as milling include tungsten carbide grades and titanium carbide grades. Tungsten carbide grades have the drawback of being more susceptible to crater wear than titanium carbide bases. To remedy this drawback, titanium carbide is added to tungsten carbide, but with the increase in the proportion by weight of titanium carbide used, the flexural strength of the cemented carbides obtained decrease. Furthermore, as compared with titanium carbide grades, tungsten carbide grades are markedly low in wear resistance when cutting steel and are prone to formation of a built-up edge, so that they are usable only under limited cutting conditions.
On the other hand, titanium carbide-base materials are widely used for high-speed cutting because they have higher hardness and more excellent heat resistance than tungsten carbide bases, but they are lower in toughness and less resistant to mechanical impact as well as to thermal impact than tungsten carbide grades. Titanium carbide grades, in addition, have lower thermal conductivity than tungsten carbide grades. When the cutting edge of titanium carbide-base material is locally heated during cutting, the edge cracks and may possibly be broken when rapidly cooled. Furthermore, when used at high speeds above a certain level or during heavy cutting, such cutting edge is prone to breakage due to the thermal stress. Because of these drawbacks, it is difficult to use titanium carbide grades for operations other than light cutting.
Thus tungsten carbide grades and titanium carbide grades have inherent drawbacks and are therefore serviceable under considerably limited cutting conditions.